NEW DEVELOPMENTS IN HIGH VACUUM APPARATUS. 

 By G. L. Kothny, Esq., Member. 



[Read at the twenty-seventh general meeting of the Society of Naval Architects and Marine Engineers, held 



in New York, November 13 and 14, 1919.] 



The adoption of the steam turbine tor marine propulsion has brought about 

 many changes in marine engineering, which have become necessary in order to fully 

 realize the many economical advantages obtainable. These changes affected par- 

 ticularly the vacuum producing apparatus. Steam turbines require the highest pos- 

 sible vacuum for highest efficiency and economy. The importance of this has been 

 realized, and considerable research work has been carried out and many develop- 

 ments have been made in relation to the condensation of steam and the extraction 

 of air. 



The principles of surface condenser design have been dealt with in several 

 papers to various societies during the last few years, many of which have shown 

 a thorough knowledge of the physical laws and practical considerations governing 

 the subject. However, very little has been said in these papers about the design and 

 development of the air pump, which is the most important part of a vacuum-pro- 

 ducing apparatus. 



It is intended in the following to record some developments which have been 

 made during the last few years in the extraction of air from marine condensers. 



The recognized limits of vacuum for well-designed marine turbine surface con- 

 densers based upon the inlet temperature of the circulating water are as follows : — 



I Yt. inch Hg. absolute with sea water at 60° F. 



2-inch Hg. absolute with sea water at 70° Y . 



2.4-inch Hg. absolute with sea water at 80° F. 



2.75-inch Hg. absolute with sea water at 85° F. 



When estimating the correct size of air pump to use, the chief factor to bear 

 in mind is the normal air leakage which the pump must handle. No definite rule 

 can be laid down for the amount of air leakage, as it depends on the size and char- 

 acter of the installation. In small installations this is relatively higher than in large 

 ones. Also in condenser installations where a large number of auxiliaries, particu- 

 larly those located on deck, are exhausted into the main condenser, the air leakage 

 is greater than in a normal installation, and a larger air pump will be required. 



Extensive investigations have shown that the normal air leakage for marine 

 surface condenser installations can be limited to the amount shown in Plate 68, pro- 

 vided that any auxiliaries exhausting into the main condenser do so at a pressure 

 slightly above atmosphere. The curve illustrated in Plate 68 is based on the total 



